Insulated containers or vessels commonly include an outer member or vessel in which an inner member or vessel is located, with the space between those vessels forming an insulating region surrounding the inner vessel. As is known heat can be transferred between the inner and outer vessel by three methods. They are conduction, radiation and convection. Air and most gases which can be disposed within the insulating space are good insulators against conduction. However, they easily convect. Thus, in an attempt to provide effective insulation, containers frequently make use of a narrow insulating space to decrease the amount of convection. Another manner for providing effective insulation is to reduce the amount of gas in the insulating space, i.e., create some vacuum therein. This action further decreases convection. In addition, with less media present it also reduces conduction heat transfer. To reduce the radiation transfer the inner walls of the insulating space can be covered with a highly reflective surface to reflect back the radiated energy. One such double wall, low pressure insulated container having with a highly reflective surface is the traditional vacuum bottle. However, traditional vacuum bottles are expensive due to having to be truly hermetically sealed. If they leak, even slowly, they lose a large part of their insulation ability. They are also typically constructed from glass or metals, because plastics are gas permeable.
Double wall insulated containers, like those described above, also exhibit a problem when subjected to the high temperatures encountered when they are washed in a dishwasher. In particular, the high heat increases the pressure of the gas volume trapped in the insulation space between the container's double walls. This is especially a problem in the case of low cost plastic containers. The increased pressure can either burst the containment or distort the container. While placing a hole in the container to vent the pressure in the insulating space to prevent such potentially damaging action is a potential solution, it necessarily allows the insulating space to fill with water or other contaminants. This decreases the vessel's insulating ability and may be a sanitary hazard.
Accordingly, a need exists for a double walled insulated container, which is formed of low cost plastic materials, to be able to withstand the rigors of repeated washings in a dishwasher, while maintaining its insulating properties and without presenting a sanitation hazard. The subject invention addresses that need.